The present invention relates to a magnetic recording medium suitable for use in a magnetic recording apparatus for magnetic recording of data by (a) heating up (applying a heat onto) a recording region of a magnetic layer (a portion of the magnetic layer) by using a light beam (heat source) and (b) by applying a magnetic field on the recording region, and to the magnetic recording apparatus using the same.
Recently, optical memories, such as DVDs (Digital Versatile Discs) and magneto-optical discs, and magnetic memories, such as hard discs, have been significantly improved to have high densities. Especially, an optically assisted magnetic recording/reproducing method has been developed as one of high-density magnetic recording/reproducing methods. For example, U.S. Pat. No. 5,656,385 (registered on Aug. 12, 1997: corresponding to Japanese Unexamined Patent Application (Tokukaihei) No. 4-176034) discloses (a) a magnetic recording medium having a recording layer made of an N-type ferrimagnetic material whose compensation point (magnetic compensation temperature) is substantially at room temperatures, and (b) an optically assisted magnetic recording/reproducing method (hereinafter, referred to as a first prior art) using the same.
For recording in this type of optically assisted magnetic recording/reproducing method, a laser beam heats up (laser heating) a recording region of the magnetic recording medium so as to sufficiently reduce a coercive force, then a recording magnetic head applies an exterior magnetic field on the recording region, thereby recording data. A region in which a recording mark (magnetic bit) is formed during the recording is limited within a region in which a region (laser beam radiation region) on which the laser beam is radiated overlaps a region (magnetic field applied region) on which the magnetic field is applied. Their positional relationship is explained referring to FIG. 17. A recording region 113 is a region in which a magnetic field applying region 111 formed by the magnetic head overlaps a heating region 112 (corresponding to a light spot) formed by radiating the laser beam. In the recording region 113, formed is a recording mark 114. As a result, it is possible to record, on the magnetic recording medium, a track 115 that has a narrow pitch that is equivalent to a diameter of beam spot of the laser beam (a diameter of the heating region 112; 0.5 m or less) by using a conventional recording magnetic head of a few m width.
Also for reproducing, the laser beam heats up a reproducing region of the magnetic recording medium so as to intensify residual magnetization, then data is read out of the reproducing region by a reproducing magnetic head. A region that is reproduced during the reproduction is also limited within a region where the region on which the laser beam radiation region overlaps a recording head region (where the recording magnetic head applies a magnetic field). This makes it possible to reproduce the track recorded with the narrow track pitch, by using a reproducing magnetic head having a large width, so that crosstalk will be restrained.
In this manner, the optically assisted magnetic recording/reproducing method, that is the first prior art, uses the laser beam as the heat source so as to selectively heat up a region narrower than the magnetic field applied region. This allows the recording track pitch to be narrower and reduces the crosstalk. For this reason, the recording and reproduction of the first prior art are carried out in high density.
Moreover, the optically assisted magnetic recording/reproducing method uses a magnetic recording medium in which an aluminum nitride (AlN) film of 60 nm is formed as an underlayer on a disc substrate, then a recording layer and a protective layer are formed on the AlN film in this order. The AlN underlayer is provided for preventing the light beam from reflecting and improving efficiency of the heating. In other words, the AlN underlayer is used for improving absorption rate of the light beam (a rate of light absorbed by the recording layer) that comes into the magnetic recording medium, and recording sensitivity.
On the other hand, an article in conference reports, K. OZAKI et al., xe2x80x9cTbFeCo as a Perpendicular Magnetic Recording Materialxe2x80x9d, J. Magn. Soc. Japan, 25, p322-327 (Publication Date: Mar. 15, 2001) (hereinafter, referred to as a second prior art) discloses a perpendicular magnetic recording medium including an underlayer having an uneven structure, for use in a conventional perpendicular magnetic recording method in which the recording is carried out only by using a magnetic head, without radiation of light. With the perpendicular magnetic recording medium, it is possible to prevent magnetic domain walls from moving, that is, to perform pinning (holding) of the magnetic domain walls so as not to move. This increases recording density. Note that an NiP layer is used as the underlayer having the uneven structure in the article.
Furthermore, an article in conference reports, Koji MATSUMOTO et al., kxe2x80x9cPerpendicular magnetic recording media using Magneto-Optical mediaxe2x80x9d, the 25th Applied Magnetization Association, p 235 (Publication Date: Sep. 25, 2001), discloses an example in which an NiP layer is used as an underlayer having an uneven structure, as the second prior art. However, this article recited that in reality a carbon layer should be provided between the NiP underlayer and a TbFeCo magnetic layer, so that exchange bonding of TbFeCo and Ni will not occur even when Ni, the magnetic body, is precipitated out.
Moreover, an article in conference reports, H. Kawano, et al., xe2x80x9cEffect of Air Gap on Write and Readout Characteristics of Magneto-Optical Media with Solid Immersion Lensxe2x80x9d, Technical Digest of Joint Moris/APDSC 2000, p188-189 (Publication Date: Oct. 30, 2000) (hereinafter, referred to as a third prior art), discloses a Magneto-optical recording medium in which an aluminum layer is provided between a glass substrate and a TbFeCo recording layer.
In data recording media, high-density recording is facilitated by increasing a recording frequency (a frequency of magnetic field application in case of magnetic modulation) so as to shorten a shortest length of a recording mark (that length of a recording mark that is along a track, where the recording mark is a minimum unit for data of 1 bit: the length represented by a reference sign M in FIG. 17).
However, in the optically assisted magnetic recording method recited in Tokukaihei No. 4-176034, the magnetic recording medium used has an insufficient capacity that makes it difficult to form a recording mark having the recording mark of the shortest length of 200 nm or less. This restrains improvement of the recording density in the optically assisted magnetic recording method.
This is based on a result of evaluation of recording and reproducing of the magnetic recording medium used in the publication. In the evaluation, it was observed that quality of signals was suddenly deteriorated when the shortest length of the recording mark approached to near 200 nm. Further, observation of the thus formed recording mark by an MFM (Magnetic Force Microscope) showed that a phenomenon in which individual recording marks are disturbed, for example, a phenomenon in which the recording marks overlap each other, or a phenomenon in which the recording mark is disappeared, was occurred when the shortest length of the recording mark approached to about 200 nm. As to a width of the track, it was observed that the width of the track got narrower and narrower, and finally was narrowed to cause a break-off. Therefore, in the conventional magnetic recording medium, the shortest length of the recording mark is practically 250 nm, considering a reliability of the optically assisted magnetic recording medium.
An exchange interaction force is one of factors that cause instability in shape of the recording mark as described above. As smaller the recording mark is, as a ratio of the exchange interaction force to forces applied on the recording mark becomes larger. In case the recording layer is made of the N-type ferrimagnetic material whose compensation point is substantially at room temperature, such as TbFeCo magnetic material, the exchange interaction force works to orient, in one direction, magnetization of the recording marks adjacent each other. Especially, in the optically assisted recording/reproducing method in which the recording region is heated up, the ratio of the exchange interaction force becomes larger during recording, because magnetic anisotoropy (coercive force) in the recording/reproducing region is significantly lowered during recording. It is deduced that an exchange interaction force caused by peripheral magnetization affects the magnetic walls (magnetic domain walls) to easily move, so that the recording mark cannot be formed, thereby causing the above phenomena. In order to stably form the recording mark in which the shortest length of the recording mark is less than 200 nm, it is necessary to have means to prevent the magnetic domain walls from moving, such as use of constraining sites (pinning sites) for stopping the magnetic domain walls from moving.
Moreover, the second prior art, which needs, in reality, three layers between the substrate and the recording layer, uses the Phosphor Nickel (NiP) layer as the underlayer for realizing the high-density recording. There is a possibility that the NiP layer may be stripped off while a spatter film is formed or with the passage of time, even though an amount of the NiP layer stripped is very small, thereby precipitating Ni, which is an component element of the NiP layer. Because Ni is also a ferromagnetic material (soft magnetic material), it is necessary to provide a carbon protective layer between the underlayer and the recording layer lest the precipitated Ni and the recording layer (magnetic layer) be bound by exchanging bonding even if this is the case. Moreover, when the laser heating is carried out for the optically assisted recording/reproducing, the stripping-off of the NiP layer is accelerated. As a result Ni is precipitated at a random location in the recording/reproducing region, and is converted into the soft magnetic material. Furthermore, this conversion is irreversible, and is not in conformity with a location and a shape of the magnetic bit in-the recording layer. For this reason, it is believed that the conversion is a factor to cause noises in reproduction signal. Moreover, it is necessary to provide a nitriding silicone layer between the underlayer and the substrate. This results in a complicated layer structure. Thus, an increase in a number of layers leads to an increase in a number of manufacturing processes, thereby hindering mass production of the magnetic recording medium. Moreover, in the second prior art, the underlayer made of Phosphor Nickel (NiP) is converted into the soft magnetic material during the heating by the laser beam. This causes a problem that the conversion affects magnetic signals of the recording layer.
Moreover, in the third prior art, the aluminum layer is sandwiched between the nitriding silicone layers so that the aluminum layer does not touch (is not put together with) the TbFeCo recording layer and is utilized as a reflection layer. For this reason, the aluminum layer has such a thick thickness of 40 nm. Moreover, unevenness in the aluminum layer deteriorates the function of the aluminum layer as the reflecting layer, thereby lowering reflection efficiency. Therefore, flatness of the aluminum layer is necessary for obtaining a sufficient reflection efficiency when the aluminum layer is utilized as the reflecting layer. For this reason, it is impossible to sufficiently prevent the magnetic domain walls of the TbFeCo recording layer from moving.
In view of the conventional problems, the present invention has an object of providing a magnetic recording medium with which high-density recording can be performed in a sufficient signal quality, and which can have a simplified layer structure, and of providing a magnetic recording apparatus using the same.
A magnetic recording medium of the present invention, in order to attain the object, is provided with (1) a substrate, and a magnetic layer, made of an amorphous magnetic material, for magnetic recording of data, or (2) a substrate, and a magnetic layer for magnetic recording of data by applying heat and a magnetic field, the magnetic recording medium further including an underlayer provided between the substrate and the magnetic layer, and the underlayer being made of a non-magnetic metal element, and being put together with the magnetic layer.
With the above arrangements, where the underlayer is made of a non-magnetic metal element, the magnetic recording layer of the present invention can have, on a surface of a layer that touches the magnetic layer, irregularities having a size (diameter of bumps) so minute, thereby limiting movement of magnetic domain walls of the magnetic layer within a shorter range (distance) (preventing the magnetic domain walls from moving more than the shorter range), compared with a conventional optically assisted magnetic recording medium. Moreover, the movement of the magnetic domain walls can be efficiently prevented, compared with the third prior art, because the underlayer is put together with the magnetic layer. As a result, the above arrangements allow a minute recording mark to be formed stably, and realizes high-density recording in a sufficient signal quality. In addition, in case where the magnetic layer is made of an amorphous magnetic material or in case the magnetic layer magnetically stores data by application of heat and a magnetic field, there is a greater tendency toward the movement of the magnetic domain walls. Thus, the above effect is distinctly exerted in those cases.
Furthermore, the above arrangements, in which the underlayer is made of a non-magnetic metal element, does not need a protective layer nor a binding layer. Because of this, the above arrangement can have a more simplified layer structure, compared with the second prior art.
Therefore, the high-density recording can be performed in a sufficient signal quality. Further, it is possible to provide a magnetic recording medium which can have a simplified layer structure.
A magnetic recording medium of the present invention, in order to attain the object, is provided with (1) a substrate, and a magnetic layer, made of an amorphous magnetic material, for magnetic recording of data, or (2) a substrate, and a magnetic layer for magnetic recording of data by applying heat and a magnetic field, the magnetic recording medium further including an underlayer provided between the substrate and the magnetic layer, the underlayer being made of a non-magnetic metal element, and having a mean thickness of 10 nm or less.
With the above arrangements, where the underlayer is made of a non-magnetic metal element, and has the mean thickness of 10 nm or less, the magnetic recording layer of the present invention can have, on a surface of a layer that touches the magnetic layer, irregularities having a size (diameter of bumps) so minute, compared with the conventional optically assisted magnetic recording medium and the third prior art. For this reason, compared with the conventional optically assisted magnetic recording medium and the third prior art, it is possible to limit the movement of magnetic domain walls of the magnetic layer within a shorter range, thereby realizing a stable formation of a minute recording mark. As a result, the above arrangements realize high-density recording in a sufficient signal quality. In addition, in case where the magnetic layer is made of an amorphous magnetic material or in case the magnetic layer magnetically stores data by application of heat and a magnetic field, there is a greater tendency toward the movement of the magnetic domain walls. Thus, the above effect is distinctly exerted in those cases.
Furthermore, the above arrangements, in which the underlayer is made of a non-magnetic metal element, does not need a protective layer nor a binding layer. Because of this, the above arrangements can have a more simplified layer structure, compared with the second prior art.
Therefore, it is possible to provide a magnetic recording medium with which high-density recording is carried out with a sufficient quality, and whose layer structure can be simplified.
In order to attain the above object, a magnetic recording medium of the present invention is provided with (a) a substrate and (b) a magnetic layer for magnetic recording of data, the magnetic recording medium further including an underlayer provided between the substrate and the magnetic layer, the underlayer being made of a non-magnetic metal element, and having an irregular surface that faces to the magnetic layer, the irregular surface having bumps of a diameter of less than 100 nm.
With the above arrangement, the magnetic recording layer of the present invention can have, on a surface of a layer that touches the magnetic layer, irregularities having a size (diameter of bumps) so minute, compared with the conventional optically assisted magnetic recording medium and the third prior art. For this reason, compared with the conventional optically assisted magnetic recording medium and the third prior art, it is possible to limit the movement of magnetic domain walls of the magnetic layer within a shorter range, thereby realizing a stable formation of a minute recording mark. As a result, the above arrangement realizes high-density recording in a sufficient signal quality.
Furthermore, the above arrangement, in which the underlayer is made of a non-magnetic metal element, does not need a protective layer nor a binding layer. Because of this, the above arrangement can have a more simplified layer structure, compared with the second prior art.
Therefore, the high-density recording can be performed in a sufficient signal quality. Further, it is possible to provide a magnetic recording medium which can have a simplified layer structure.
Note that in the specification of the present application, the terms xe2x80x9cdiameter of bumpsxe2x80x9d mean how much is the diameter of the bumps that are higher sections with respect to a level of a bottom surface of the non-bumps. Moreover, in the specification of the present application, the wording the xe2x80x9cbumps of a diameter of less than 100 nmxe2x80x9d means that a mean value of the diameter of the bumps is less than 100 nm.
In order to attain the above object, a magnetic recording apparatus of the present invention for magnetically recording data onto any one of the magnetic recording media, the magnetic recording apparatus magnetically recording data onto the magnetic layer, and including magnetic field applying means for applying a magnetic field on the magnetic layer, the magnetic field orientating magnetization of the magnetic layer.
The above arrangement can provide a magnetic recording apparatus that can perform high-density recording in a sufficient signal quality because the magnetic recording medium having the above described feature is used.
In order to attain the above object, a magnetic recording apparatus of the present invention for magnetically recording data onto any one of the magnetic recording media, the magnetic recording apparatus magnetically recording data onto the magnetic layer, and including (a) light beam radiating means for radiating a light beam locally onto a portion of the magnetic layer, the light beam locally heating the magnetic layer, and (b) magnetic field applying means for applying a magnetic field on at least part of the portion of the magnetic layer on which the light beam is radiated, the magnetic field orientating magnetization of the magnetic layer.
The above arrangement can provide a magnetic recording apparatus that can perform high-density recording in a sufficient signal quality because the magnetic recording medium having the above described feature is used. Moreover, with the above arrangement, where the optically assisted magnetic recording method is applied, a region in which the recording is performed is limited within an area (region) in which a light beam radiating region overlap a magnetic field applying region. This narrows a recording track width, thereby realizing high-density recording. Furthermore, there is a greater tendency toward the movement of the magnetic domain walls in the optically assisted magnetic recording method. Thus, the above effect is distinctly exerted in those cases.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.